This invention relates generally to rotary combines. It relates particularly to the cleaning system in a rotary combine, and the separation of grain and MOG (material other than grain) after it passes through the combine""s threshing concave and separating grates.
In most conventional rotary combines, the grain and MOG which pass through the threshing concave fall to a grain bed having screw conveyors for to conveying the grain and MOG rearwardly. At the rear of the grain bed, the grain and MOG together enter a cleaning system. The forward end of the cleaning system is near the fore-to-aft midpoint of the rotary threshing and separating assembly. Because the grain and MOG are collected together on the grain bed and conveyed by the screw conveyors, they become mixed and it is difficult to separate MOG from grain. As a result, either large quantities of MOG are deposited on the chaffer sieve of the cleaning system, along with the grain, or grain is blown out the rear of the combine enmeshed in a clump of MOG. This problem is exacerbated as the moisture content of the MOG increases.
In most rotary combines, a grain bed or its equivalent is provided below the separating portion of the rotary threshing and separating assembly. A conveying mechanism, such as screw conveyors, then conveys grain and MOG forward and deposits it either directly on the chaffer sieve or on the grain bed. In the latter case, screw conveyors in the grain bed then convey all of the grain and MOG rearwardly and deposit it on the chaffer sieve. In such machines, all of the grain and MOG which passes through the rotary threshing and separating assembly is deposited on the chaffer sieve of the cleaning system with grain and MOG intermixed. As a result, the cleaning system receives, and must process, almost all of the material which passes through the threshing concave and separating grates, untangling and separating MOG and grain as it does so. Consequently, in many crop conditions the cleaning system in such rotary combines is the limiting factor as to throughput.
In most conventional rotary combines, tailings are collected in a tailings auger which is located at the rear edge of the shoe sieve. The tailings, which may constitute up to 10% of the combine""s throughput, are then elevated and recirculated into the rotary threshing and separating assembly. Since the tailings are being added to the material from the field, the assembly now must process 10% more material than it originally received from the field. On the next pass, the tailings are again recirculated into the assembly. The assembly then has to process 11% more material than it received from the field. As the combine continues to operate and the tailings continue to be recirculated, the total amount of material being sent to the rotary threshing and separating assembly increases geometrically, and eventually the load may stall the assembly.
It is an object of the present invention to provide an improved cleaning system for a rotary combine.
It is another object to provide a cleaning system which is effective to separate a high percentage of the MOG from grain and blow it out onto the field before it even reaches the chaffer sieve.
It is still another object to provide a cleaning system which effectively prevents overloading of the threshing and separating assembly with MOG.
It is a further object to provide a cleaning system which increases the throughput capacity of an axial-flow, rotary combine.
It is yet a further object to provide a cleaning system which recycles tailings onto the chaffer sieve in an optimal pattern regardless of whether the combine is operating on a side hill or on level ground.
It is yet another object to provide a simpler cleaning system, which has fewer moving parts and is less costly; a system which is more robust and operates well under all crop conditions and with all crops.
It is still another object to provide an improved grain cleaning method.
The foregoing and other objects are realized in accord with one aspect of the present invention by providing a rotary combine including a frame in which a longitudinally extending threshing and separating assembly is mounted. The threshing and separating assembly includes a threshing chamber having a threshing rotor rotatably mounted therein. The chamber and the rotor each include a threshing section and a separating section which cooperate to thresh and separate the crop. When the rotor is rotated relative to the chamber, grain and MOG are forced through the concave and grate of the chamber along substantially the entire length of the rotor.
Below the longitudinally extending threshing and separating assembly, a longitudinally extending cleaning system is supported on the combine frame. The cleaning system extends substantially the length of the threshing and separating assembly. It includes a horizontally elongated air passage which extends from front to rear below the threshing concave and separating grate and above the chaffer sieve of the longitudinally extending cleaning system.
The longitudinally extending threshing and separating assembly is inclined upwardly from the horizontal, front to rear, at an angle of about ten degrees. The sieve components of the longitudinally extending cleaning system below it are inclined upwardly, front to rear, at an angle of about five degrees. As a result, the aforementioned horizontally elongated air passage has a vertical dimension which is greater at the rear than at the front, i.e. the passage widens vertically as it proceeds rearwardly.
The longitudinally extending cleaning system of the invention includes a fan for generating a high velocity stream of air. The stream of air is directed upwardly and rearwardly through the vertically widening air passage. The stream of air is discharged from the combine through a MOG discharge port at the rear of the combine. The discharge port opening is large enough to permit the high velocity stream of air to leave the rotary combine unimpeded, carrying MOG with it for discharge to the field.
The air stream velocity generated by the fan is high enough that the MOG is carried with it and discharged through the MOG discharge port. However, the velocity is not so high that grain, which falls through the longitudinally extending threshing concave and separating grate, is carried along. Thus, the grain continues to fall through the stream of air to the underlying chaffer sieve.
According to one embodiment of the invention, the cleaning system of the invention incorporates a grain shaker pan located under the forward portion of the threshing concave. The chaffer sieve is immediately behind, and below, the grain shaker pan whereby an aperture having a vertical projection is defined between the rear edge of the shaker pan and the front edge of the chaffer sieve. A high velocity stream of air flowing through the aperture pre-cleans grain cascading over the rear edge of the grain shaker pan onto the chaffer sieve.
According to another embodiment of the invention, the grain shaker pan is omitted in favor of a downwardly sloped, stationery grain deflector below the extreme forward portion of the threshing concave zone. The chaffer and shoe sieves of the cleaning system extend forwardly closer to the front end of the threshing concave in this embodiment.
Regardless of the embodiment utilized, the air stream is generated by a fan in a housing which extends transversely across the front of the cleaning system. The housing includes a bottom panel which has a scroll shape. A top panel is arranged above it. Between them they define a fan outlet conduit. Because of the scroll shape, the conduit is long but compact so it can be received in available space within the combine.
According to the method of the invention, threshing and separating of grain from a crop is provided by the steps of feeding the crop into an axial flow, rotary threshing and separating assembly; moving the crop along a helical path through the rotary threshing and separating assembly in multiple passes over its threshing concave and separating grate; directing an uninterrupted, free flowing air stream below and along the length of the threshing and separating assembly so as to carry MOG along in the air stream for the length of the assembly; discharging the air stream along with the MOG that has been picked up and carried in the air stream; and collecting the grain which falls through the air stream along the length of the threshing and separating assembly.